Technical Field
The present disclosure relates to a communication device, program storage medium, and method, applicable, for example, to a communication device that receives frames intermittently.
Related Art
For example, IEEE802.15.4 defines various additional functionality for a MAC layer, and includes coordinated sampled listening (CSL) technology as one intermittent reception method for receiving frames intermittently in order to achieve savings in power (see, IEEE Std 802.15.4e™-2012 (IEEE Standard for Local and metropolitan area networks Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs) Amendment 1: MAC sublayer) 5.1.11.1 Coordinated sampled listening (CSL) (referred to below as IEEE document)).
Simple explanation follows of a procedure for data frame communication between a transmitter and a receiver including CSL compatible communication devices.
The transmitter attempting to transmit a signal including data frames, first, in an asynchronous transmission mode, continuously transmits a signal including a wakeup frame prescribing a data frame transmission start timing (rendezvous time) during maximum CSL reception periods (max CSL Period), and then the transmitter transmits the data frame after the period of time of the max CSL reception period has elapsed.
The receiver adopts a state of awaiting reception only for the duration of wakeup frame reception segments in the CSL reception periods, and does not perform reception actions at other times. If the receiver is able to receive wakeup frames while awaiting reception, then data frames can be received from the transmitter by transitioning to the state of awaiting reception immediately prior to the rendezvous time.
When an acknowledgement (ACK) is requested in return for receipt of the data frame, the receiver returns an ACK including the CSL reception period of the receiver and the rendezvous time that is in the received wakeup frame (namely, a CSL phase indicating the misalignment between a timing of synchronization information in the wakeup frame and a reception timing).
If the transmitter has not received an ACK from the receiver, the transmitter re-transmits the wakeup frame and the data frame to the receiver in the asynchronous communication mode at the next data frame transmission timing.
On the other hand, the transmitter has received an ACK from the receiver, the transmitter saves the CSL reception period and the CSL phase of the receiver, and performs synchronization correction with the receiver. Then, when transmitting the next data frame, the transmitter transmits the wakeup frame and the data frame in synchronous communication mode at the corrected transmission timing.
In the IEEE document, there is no particular stipulation of the number of times for transmitting the wakeup frame when in the synchronous communication mode. The number of times that the wakeup frame is transmitted in periods of synchronous communication can be much less than in periods of asynchronous communication, and this is preferable. This is because it is sufficient to transmit the wakeup frame only the number of times that enables synchronization correction. For example, say the wakeup frame transmission period in the asynchronous communication mode is 1000 milliseconds, then the wakeup frame transmission period in the synchronous communication mode can be set at from 1/100 to 1/10 of that in the asynchronous communication mode, so as to be, for example, 100 milliseconds or less. For example, suppose the transmitter transmits the wakeup frame three times, and synchronization is achieved as an ACK response of the CSL phase is recognized in the second frame. In this event, it can be determined that the receiver side is behind if the ACK response is in the first frame, and the receiver side is ahead if the ACK response is in the third frame.
However, if the wakeup frame transmission period is short, then it is possible that transmission of the data frame fails even if there is only a slight synchronization misalignment between the transmitter and the receiver.
Moreover, since the wakeup frame transmission period is much longer in the asynchronous communication mode than in the synchronous communication mode, frequent occurrences of frame transmission when in asynchronous communication lead to power consumption in the transmitter, and are liable to greatly increase the communications load on the overall network.
Thus the present disclosure provides a communication device, program storage medium, and method to achieve a shorter control frame transmission period (wakeup frame transmission period) in total, while synchronous communication is maintained.